This 2D opening convention is both offensive and defensive. The frequency is high since you quite often have a 5 card major-suit with 3-10 HCP. It's really fun to see your opponents trying to guess what you have when they are strong. If you have played Multi before, you will find many similarities, but the responses is made more flexible so you have better chance to find a fit.

THE 2 DIAMOND OPENER MAY HAVE:
- 3-10 HCP. 5 card major. You shouldn't have a side-suit in the other major suit, but hey, if you want to have fun. In first/second spot strength is 3-8. (not invitational strength vs 15-17 NT). There are NO requirements for trump quality. 65432 is good enough. 4 card minor is OK and preferred, but 5-5 is OK just if majorsuit isn't very weaker than the minor suit.
- 25-27 HCP. Balanced. (At least 8 1/2 playing tricks)
- 6+club without side suit. Game forcing.
- 6+diamond without side suit. Game forcing.

Those strong hands in the multi means that you can adjust the 2C opening and make it more precise. Woodgroves 2C has these changes in the system. Take a look.

RESPONSES TO 2 DIAMOND OPENING:
Pass: you take a chance that your partner has weak 2 (if not he will kill you!). Responder has (maybe) diamond and a short suit in one of the major suit. Let your opponent guess.
2H: Not game if weak 2 in heart.
2S: Invitational if weak 2 in heart.
2NT: Lebensohl. Minor suit to play at the 3 level, or 6+card major
suit and invitational. Requests 3C bid from partner.
3C: Artificial forcing bid. Asks for opener to describe his hand.
3D: Preempt in partners weak 2 suit.
3H: Natural game forcing.
3S: Natural game forcing.
3NT: To play.
4C: Preempt in minor suit. At least 5-5.
4D: Preempt in partners weak 2 suit.
4H: To play if weak 2.
4S: To play if weak 2.

RESPONSES TO 2D - (Dobl)
Pass: I want to play in diamond. This bid may be a tactical bid hoping your opponents on your left will take out. Your pd will take a good look if the double is passed to him.
Rdobl: Bid your weak 2 suit.
2H: To play.
2S: To play.
Otherwise the responses are as without interference.

RESPONSES TO 2D - (D) - Pass - (Pass)Remember bridge is also psychology. If you can feel your opponents are loving to play against 2D, you should run, even with 4 diamonds. Pd may have a difficult hand to bid, and hope they would bid.
Pass : 4/5 Diamonds.
Redobl : 5-3 or 5-4 in the major suits.
2H : 5 Heart & 4/5 Clubs.
2S : 5 Spades & 4/5 Clubs.

RESPONSES TO 2D - (2H/2S)
Dobl: Request partner to pass with weak 2 in the overcalled suit.
Otherwise the responses are as without interference.

OTHER OVERCALLS from 2NT -->
Doubl: Penalty
3H/4H: If pd hasn't had the chance to bid earlier, the H bid ask opener to correct if weak 2 spade.